All individuals aged 20-84 years from 1 January 2005 to 31 December 2011, who have been enrolled with their primary care physician for at least 2 years and have a computerized prescription history of at least 1 year. Patients will have to be free of acid-suppressing drugs (PPI or H2RA) for at least one year, and never have a diagnosis of cancer, alcohol abuse or alcohol-related disease, or drug abuse.